Chronometric electronic radiosonde system



April 26, 19497A c. M.` HAMMEL 2,468,703

CHRONOMETRIC ELECTRONIC RADIOSONDE SYSTEM Filed Sept. 26, 1946 8 Sheets-Sheet 1 Pz/sffa/w EELHXAYNOA/ y Osc/nvrae Lh/Z [2M IN V E TOR.

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CHRONOMETRIC ELECTRONIC RADIOSONDE SYSTEM INVENTOR.

April 26, 1949. c. M. HAMMEI. l 2,468,703

CHRONOMETRIC ELECTRONIC RADIOSONDE SYSTEM Filed sept. 26, 1946 8 shets-sheet 3 4'Apr-il 26, 1949. c. M. HAMMEL 2,468,703

CHRONOMETRIC ELECTRONIC RADIOSONDE SYSTEM v TOR. L M* u@ Ap 26, 1949. c. M. HAMMEL GHRONOMETRIC ELECTRONIC RADIOSONDE SYSTEM Filed Sept. 26, 1946 8 Sheets-Sheet 6 I I I IWWOHWMIIEWWW Mllmdl TMWNWWM .WIMJNSS www [TTU um Q\ .IIIINIIIII mgm . April 26, 1949. c. M. HAMML i 2,468,703

CHRONOMETRIC ELECTRONIC RADIQSONDE SYSTEM I Filed sept. 26, 1946 a sheets-sheet 7 /NPur Feo/w @ECE/VEB Y I CL# L l BY q- April 26, 1949.l c. M. HAMMEL CHRONOMETRIC ELECTRONIC RADIOSONDE SYSTEM Filqd sept. 25, 1946 8 Sheets-SheetI 8 b. mali. To -u WML w m V m W/MP T Mv K VIII Jan Patented Apr. 26, 1949 I UNITED STATES PATENT* oF-FICE CHRONOMETRIC ELECTRONIC RADIO- SONDE SYSTEM Cliiord M. llammel, Winchester, Mass., assignor f .to Serdex, Inc., Boston, Mass., a corporation of Massachusetts Application` September 26, 1946,'Serial No. 699,373

x Claims.

. signals responsive to changes in meteorological conditions including pressure, temperature and relative humidity. One form of apparatus has generally been constructed and arranged to transmit a reference signal followed by three intelligence signals which are in turn followed by a second reference signal, thus forming a iive element cycle which is repeated every four or ilve seconds. Each ground station is provided with a receiver and mechanical means for printing marks on a slowly moving sheet of scaled paper in such a way that the linear distance between themark representing the reference'signal and the marks representing the intelligence signals are functions of values of pressure, temperature and humidity. Several dilculties have been encountered in the construction and operation of radiosonde equipment of this chronometric character. For example, the voltage output of the battery used to power the airborne equipment is subject to diminution during the period of flight with consequent change in the speed of the timing mechanism. Furthermore the wide v changes in temperature and pressure encountered for recording.

Another object of the invention is to provide apparatus for continuously and simultaneously transmitting and recording measurements of pressure, temperature and humidity.

An important feature of the invention consists in providing electronic means for continuously transmitting and recording meteorological information in contrast to the discontinuouselectro-mechanical systems now in use in which several seconds necessarily elapse between corresponding points in consecutive cycles of operation.

Still another feature of the invention consists in a combination of elements by means of which the ground station is made to react only to vsignals transmitted from .the balloon, all extraneous signals being barred, and by means of which circuits responsive to the intelligence signals are automatically synchronized.

l Another feature of the invention resides in providing at the ground station separate circuits for recording values of pressure, temperature and humidity, which are so arranged that there can be no overlapping. That is to say, the pressure circuit, for example, will never react to anything but pressure signals and not be eiected by temperature or humidity signals or by the reference signals.

Still another feature of the invention resides in means for employing the synchronizing reference signal in conjunction with an automatic radio direction finder.

These and other objects and features of the invention will be more readily understood and appreciated from the following detailed description of a preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawings, in which:

Fig, 1 is a diagram illustrating -by a succession of curves the pulses transmitted by th airborne equipment during one cycle, together with curves showing the composition and origin of the transmitted pulses, l

Fig. 2 is a diagram similar to that shown in Fig. l but illustrating the treatment by the ground stationvv apparatus of the received pulses,

Fig. 3 is a block diagram of the units comprising the airborne equipment, y

Fig. 4 is a 4block diagram of the units'comprising the ground station equipment.

Fig. 5 is a diagram of the pulses from the early4 Fig. 8 is a circuit diagram of the discriminator at the ground station, and

Fig. 9 is a circuit diagram of one `channel at the ground station.

y.to the trailing edgesl of. thebroader pulses fduced by the multivibrators. The pulses from the differentiating circuits and from the re1aical l'tion oscillator'are .amplied and used to lteyl a yradiofrequencyoscillatorconnected to anan i,

' Before proceedlugto a detailed description of l rst discussl brieny the. general organization -1-1 thereof. .In the airborne equipment I include l four 'delay type multivlbratorl `units,triggered by a relaxation. oscillator which also locks theml in.

proper synchronization. The rst delay multivibrator-is utilized to transmit a pulse for timey lreference purposes, thek delayl being relatively; 1, .short so thatit will follow closely the pulse origihated by the relaxation oscillator.

The other the .elements Acomprising `my. invention..r I shall three delay multivibrators are controlledpartly l .l

pressure.. The routpu pulses of the four delay jrnultivibrators are fed through ldifiere:itiating l circuitswhich` produce short puises correspon iing tenna.

'l'Thegroundstation equipmentincludes a ire.y

nel. l l l "Functions or airborne .unirl f l I shall now discuss the Aairborne equipment in. ltermslof lits functions andwith reference t Figs.; 1 and 3. Theblock diagram of Fig` fishows the g by the relaxation' escmator 'anar-army by ele#y ments responsive tol temperature, lhumidity and.

` keyer- 1.4, and then to. the RF oscillator I5. The

last curveof Flg.1 shows the vepulsescompriselements in the airborne unit and their functional relationship, while the diagram of Fig. 1 shows the various pulses produced and transmitted. Fig. 7 shows one form of circuit suitable for the airborne equipment and will be discussed later.

The rst element is n. relaxation oscillator I0,

obtaining power from a suitable battery (not r shown), carried by the balloon and arranged to deliver a short negative pulse at fixed intervals. I have found that a frequency of 200 cycles per second conveniently adapts itself to the conditions encountered. The relaxation oscillator I0 is therefore constructed to deliver a pulse every 5000 microseconds, the pulse lasting for about 2 microseconds.

The output of the oscillator I0 is represented in the curves of Fig. 1 by the negative pulse I2 and is sent directly to a pulse amplier and keyer I4 which feeds a radio frequency oscillator IB connected to the balloon antenna.

The output of the oscillator I0 is also fed to four delay multivibrators I8, 20, 22 and 24. The delay multivibrator is a pulse generating circuit which is set in action by an exciting trigger potential derived from an external source. Once the delay multivibrator has been triggered, it will produce a rectangular pulse of a width (time) determined by the circuit constants. The delay multivibrator I8 is constructed with xed constants and extinguishes after a predetermined interval with respect to the triggering pulse. The second curve of Fig. 1 illustrates the positive pulse the trailing edgel of each pulse trom thel multll 'vibratorsris far greater than any change'prececlinglor `following the. trailing edge, there'su'ltis: l :,n a singie,k peaked, negative pulselas shownin Fig.l

' 1 and` lasting about: .imicrosecond The same reference characters are used to designate lthe 1 I i pulses throughout the descri t on ofthe system in 'The- .delay `multivibrator 20, isl rsimilarA to ther f reference Amultivibrator Ilexceptthat; lt .includes a negativey ternperaturel coeilicient .resistor 2|.'

iwhichvaries. in its resistance asa fun in" of ambient 'temperature and controls lthe period of` terminen range.l

Similarly. the delaymultivibratery22l is con-A I9 produced bythe reference delay v,niultivilcrater l l n l 'the durationl or the Apuise :s produced by' the de- -laymultivibrator 20 but only through a prede'- knectedto a resistorstrlp and Ato a kcontact 'moved I across the strip by a humidity responsive element such as la' conned diaphragrnof goldbreater's y @skin l(not. shown) ysol that its'pulse width'26 or f l f rperiod ci delay is responsive to humidity.. yI fikewise a pressure capsule of conventional structure l (not shown) isalso arranged to vary the position l f of a 'contactor -aresistor Strip includedin the circuitr of'the multivibrator 24 to kcontrolothe width of its pulse 21. l

The positive pulseA output of 'each of ltheA ,delayy y y multivibrators lis passed through a' 'difEerentiat--. :Q l Qing circuit which produces a negative pulse measf l u'ring therate fofchange; in 'the' output of' t1^e multivibrators. Since the rate of: r' a ge 'along .l

- order tomake it easiertofollow what happens.

y After, thepulses .passthrough'the'dliferentiat-A l :.LA ing circuits, they are fed to'the'amplliier. and

ing the completecycle;l the xedfrequency synchronizing: and reference pulses lI2 and i9; and

the cycle,ibut ktluaconstants for the delay multi-l vibrators 20, 22 and 24 are so selected that the ranges of delay cannot overlap. That is to say, as set up in the drawings the sequence of synchronizing pulse, reference pulse, temperature pulse, humidity pulse, and pressure pulse, is unvarying. Obviously the exact sequence used is a matter of choice.

It is to be understood that the resistors included in the delay multivibrator circuits 2U, 22 and 24 and responsive in value to movements of the elements sensitive to temperature, humidity and pressure are so selected that the variations possible in each case produce an effective range for each of the three multivibrators. These ranges are indicated in Fig. 1: as before stated the circuit'constants are such that the ranges cannot overlap, but it is evident that as the ambient temperature changes, for example, the trailing edge of the pulse 25 will move back and forth within the range indicated on the drawing. That is to say, each position of the trailing edge of the pulse 25 within its range corresponds to a temperature value, and the elapsed time between the pulse I2 and the trailing edge of the pulse 25 is the measure of temperature. The same considerations apply to the pulses 26 and 21 referring to humidity and pressure values. To obtain a` satisfactory circuit the design of the unit must be such that the synchronizing pulse I2 is at least twice Vas wide, or twice as long in duration, as the widtnof the intelligence pulses. For example, the pulse I2 may beir two microseconds in duration and the e pulses corresponding to the trailing edges of the multivibrator pulses should then be in the order of one microsecondin duration. The relative values 4appear in the last two curves of Fig. 1,

although it must ybev understood that this figure is not drawn to scale.

Circuit of the airborne unit I have treated the airborne unit from the functional standpoint. and skilled electronic engineers will readily appreciate that any one plates of a double triode.

of a number of different circuits could be used to obtain comparable results. For example. there are many kinds of relaxation oscillators which could be employed to trigger the delay multivibrators. I have, however, designed a. circuit for the airborne unit, which is the best form known to me for carrying out my invention. This circuit is shown in Fig. 7 which will now be discussed in detail.

The relaxation oscillator I0 comprises a blocking oscillator constructed according to wellknown principles and per se forms no part of my invention. For a thorough discussion of the factors involved in constructing an oscillator of the type required for the airborne unit, the reader is referred to an article appearing in Radio News for September 1946, volume 36, No. 3, beginning on page 14. As explained previously, the pulse from the oscillator I0 should be twice as wide as the diiferentiated pulses from the delay multivibrators, and the aforesaid article includes all the information necessary to construct an oscillator so characterized.

The delay multivibrators I8, 20, 22 and 24 are all identical except for the provision of variable resistors in the last three. Here again the circuit itself does not form part of my invention, and the reader is referred to Theory and Applications of Electron Tubes, by Herbert J. Reich, published in 1944 by the McGraw-Hill Book Co., Inc. On page 360 of this book a circuit is shown which could b'e used in place of the one shown in Fig. 7 and which differs from the circuit of the multivibrator only in the fact that the latter is condenser coupled between the plate of the first triode and the grid of the second, whereas the circuit in the book employs resistance coupling. As shown in Fig. 7 the output of the multivibrator 20 is fed through a differentiating circuit which comprises a condenser and resistor connected in series from the plate of the second triode of the multivibrator 20 to ground, the output from the differentiator being taken from between the condenser and the resistor. The operation of the differentiator circuit 35 is well explained on page 357 of Reichs book above referred to.'

The amplifier and keyer is less conventional and will, therefore, be described in some detail. It comprises essentially a triode, for example, a 604, and the output from the differentiator circuits is combined with the output from the oscillator I Il and fed to its control grid. The control grid is connected to B+ througha bias resistor so that the tube is normally in a conducting state. When the negative pulses from 'the differentiator circuits and the relaxation oscillator I0 reach the control grid, each pulse momentarily biases the tube beyond cut-oil. Consequently a positive pulse appears on the plate of the 604 every time a negative pulse is received on the grid. The output of the keyer and amplifier I4 is inductively coupled to the in the RF oscillator I6.' The latter is a conventional tuned plate push-pull oscillator wherein the only source of plate voltage is the pulses received from the keyer Il. The result is that the 6J6 tube will osciliate only upon the receipt of positive pulses in the plate circuit. Those skilled in the art will readily appreciate that the frequency allotted for radiosonde work will necessarily have a modifying influence on the circuit of the RF oscillator.

It will be observed that coupling condensers I1 are inserted in the line from the relaxation oscillator I0 to the multivibrator circuits i8, 20, 22 and 24. Their function is conventional. Similarly, coupling condensers I5 are inserted in the lines from the diierentiator circuits to the amplifier and keyer Il; the coupling condensers I6 are preceded by series connected isolating resistors I3. Again, the functions of the coupling condensers I5 and the isolating resistors I3 are conventional.

Functions of the ground station Broadly speaking the ground station comprises equipment for receiving the pulses sent from the balloon and recording the time diiferentials between the reference pulse I2 and the intelligence pulses 25, 26 and 21 in terms of voltage so that recording voltmeters may -be calibrated in terms of the meteorological variables being measured. The iirst element in the ground station equipment is a high frequency receiver |00 connected to an antenna and"tuned to receive the signals sent from the RF oscillator I6 in the airborne uni-t. As shown in Fig. 2 the receiver pulse output corresponds to the output of the oscillator IIS as shown in the-last line of Fig. 1 except that the pulses are negative.

There are four Ichannels, or distinct circuits, in which the received pulses are treated and converted as will later appear, and the output of the receiver is fed directly into the input tube of each of lthe four channels. There is also provided a discriminator |02 into which the output of the receiver |00 is fed. The discriminator eliminates all of the pulses except the two microsecond pulses I2, originating in the relaxation oscillator IIJ, which are then fed into a radio direction finder system |04. The latter forms no part of the present invention, per se, but is preferably constructed according to well-known princples and is automatic in operation. The radio :direction finder system operates lto indicate the azimuth and elevation angle of the balloon in flight. While the circuit for the radio direction finder system, as stated above, is not a part of the present invention,l it is very definitely an important feature of my invention to operate the direction finder solely by the synchronizing vpulses I2 sent out from the balloon. By operating the radio direction nder with pulses sent at a i'lxed frequency, and by barring from the direction finder all other signals, the direction nder is made to perform its -functions much more eiliciently than would be possible by operating it on heterogeneous pulses of random frequency. It may happen that `an extraneous signal will coincide with the pulse i2, but statistically the likelihood of such an event is extremelysmall; furthermore no harm would be done if a pulse I2 did occasionally coincide with the extraneous sigrectify :any error.

ananas yshows the functional relationship of the elements yo1' the ground station and a detail of the units comprising the channel for the humidity pulse 26. It m to be understood that the other channels are substantially identical.

The output of the receiver is fed to a buffer -and clipper circuit |06 which isolates the receiver from the elements following the buffer and clipper and which also -limits all of the pulses to a predetermined value as represented by the last line of Fig. 2. The output of the buffer and clipper |06 is then fed to a pair of video gate circuits |06 and ||0. The video gate circuits are in effect amplifiers which function only when exciting voltage is applied from two external sources at the same time and are otherwise biased beyond cut off by a suitable negative voltage on the suppressor grid. That is to say. the output from the buifer and clipper |06 is not sufficient in itself to -actuate either of the video gate circuits.

The output of the discriminator |02 is fed, in each channel, to a buffer circuit ||2 which isolates the channel from the discriminator and which amplifles the pulses l2 coming from the discriminator |02 and feeds thefm as trigger pulses to a delay multivibrator |14 having circuit constants selected to give a delay period corresponding to one of the delay multivibrators 20, 22 or 24 of the airborne unit; for example, the delay multivibrator ||4 may be set to correspond to the period of the delay multivibrator 22 of the airborne unit, considering that the channel shown in detail is that used to treat the .pulse 26 corresponding to humidity. The output of the delay multivibrator ||4 is fed to a differentiating and buffer circuit I6.

The diiferentiator ||6 differentiates the pulse from the delay multivibrator H4 which appears in Fig. 2 as the pulse 26', since it corresponds to the pulse 26 from the multivibrator 22, and converts it' into a sharply peaked negative pulse 26" corresponding to the trailing edge of the .pulse from the delay multivibrator III. The output from the diilerentiator is fed through the buffer into an early gate ||8 comprising a trigger circuit which will iire only when excited from an external source such as the output of the differentiator ||6. The early gate pulse ||9 isfed into a late gate circuit |20, also a trigger circuit ar- 'ranged to fire only when triggered from an external source such as the early gate circuit IIB. The circuit constants of the gate circuits H8 and are so selected that the early gate pulse ||6 triggers the late gate circuit |20 in time to produce an overlapping pulse |2I. The overlapping of the early gate pulse I9 and the late gate pulse |2| is sh-own diagrammatically in Figs. 5 and 6.

The pulse IIS from the early gate ||8 is also fed into the video gate circuit |08, and the pulse |2| from the late gate circuit |20 is fed into the video gate circuit I0. As before stated, the video gate circuits |08 and ||0 are so constructed that they will not conduct unless excited by two external coinciding signals, one -comprising the pulse from the buffer and clipper |06 and the other from the early and late gate circuits H8 Vand |20. While the buffer and clipper feeds into the video gate circuits all of the pulses from the receiver |00, the video gate circuits only conduct when a pulse from the buffer and clipper coincides with early and late gate pulses from the circuits i I6 and |20. The latter pulses are obtained from the delay multivibrator Hl which, as previously stated,A is designed to give a pulse 26 coinciding with the pulse 26 from the humidity delay multivibrator circuit 22 in the airborne unit. Consequently the video gate circuits |06 and ill and the units which follow them are in effect actuated only by humidity pulses 26. The video gate circuit |08 leads to an integrator circuit |12 and the gate circuit ||0 leads to an,integrator` circuit H3. The combined output from the`in tegrator circuits I l2 and l I3 is fed into a cathode follower amplier |22. The arrangement of the cathode follower amplifier |22 and the integrator circuits I2 and H3 is such that thevD. C, voltage output from the cathode follower |22 swings `ne way or the other in response to the character of the output of the integrator circuits. The integrator circuit ||2 influences the voltage output in the negative direction, and the integrator circuit ||3 influences the voltage output positively. Figs. 5 and 6 illustrate the three possible relative positions of the humidity pulse 26 from the buffer and clipper |06 in relation to the pulses from the early and late gate circuits ||8 and |20. Il. the pulse 26 rides evenly on the pulses ||9 and |2|, the integrator circuits ||2 and ||3 will respond evenly and three will be no change in the voltage applied to the input of the cathode follower |22. If the humidity signal pulse 26 shifts its position so that it rides more on the early gate pulse H8 than on the late gate pulse |2 the integrator circuit i2 and the video gate |08 will deliver negative voltage to the cathode follower |22 while the video gate ||0 and the integrator ||3 will supply to the cathode follower |22 a positive voltage corresponding only in proportion to the pulse I2 Consequenly the cathode follower |22 will swing more negative. Conversely if the pulse 26 shifts so that it rides more on the late gate pulse |2| than on the early gate pulse IIS, the video gate l0 and the integrator |3 will swing the cathode follower |22 in the positive direction. The output of the cathode follower |22v is fed back to the delay multivibrator ||4 where it is applied as a bias voltage to vary the delay period of the multivibrator. When the signal pulse 26 occurs early and rides on the early gate ||9, the cathode follower |22 will apply to the delay multivibrator ||4 a bias tending to shorten the delay period. As a result the trigger pulse to the early and late gate circuits from the delay multivibrator III will be made to occur a little earlier and both gate pulses ||0 and |2| will be shifted to the left with respect to the graph shown in Figs. 5 and 6, and the result will be to move them until the pulse 26 rides evenly spaced with respect to the pulses from the early and late gate circuits. Similarly if the signal pulse 26 rides more on the late gate pulse |2|, the video gate circuits with the integrator circuits and the cathode follower |22 will apply a biasing voltage to the delay multivibrator ||4 tending to lengthen the delay period and shift the early and late gate pulses to the right with respect to Figs. 5 and 6 to again bring about a condition where the signal pulse 26 is evenly spaced with respect to the early and late gate pulses ||9 and |2|. This means that the trailing edge of the pulse from the delay multivibrator Ill occurs at the same time as the signal pulse 26 and will follow any change that the pulse 26 mightmake. Since the position of the delay multivibrator pulse is a function of the voltage from the cathode follower |22, it follows that this yoltage is proportional then to relative humidity.

The output from the cathode follower appears as a direct current voltage and is fed through a voltage compensating circuit |24 to a recording voltmeter |26 which effectively measures the output of the cathode follower |22. The recording voltmeter |26 may be calibrated in terms of relative humidity and from the foregoing explanation it will appear that the recording voltmeter |26 is continuously supplied with a voltage proportional to relative humidity being measured continuously by the sensitive element in the balloon. Furthermore the value recorded by the voltmeter |26 is corrected 200 times every second.

Recognizing that the radical changes encountered in meteorological conditions as the' balloon ascends may tend to introduce 'changes of rate and errors of measurement, I provide means for continuously compensating for the eect on the instr-ument of all changing conditions. I'hat is done by utilizing the second reference pulse I9. It will be remembered that the second reference pulse is obtained from the delay multivibrator I8 carried by the balloon and triggered by the relaxation oscillator I0. 'I'he elements of the multivibrator circuit I8 are of fixed value, as opposed to the variable elements included in the intelligence multivibrators 20, 22 and 24. Hence the timing between the trigger pulse I2 and the second reference pulse I9 will remain at a constant value except as affected by extraneous conditions. Any change in the elapsed time between the pulse I2 and the pulse I9 will be the result of an error which equally affects the ticming between the pulse I2 and all of the intelligence pulses 25, 26 and 21, It follows that if means is provided for changing the period between the pulse I2 and the pulse 26', for example, in the same amount as any change appearing between the pulses I2 and I9, a proper correction will have been inserted. That is the purpose of the second reference pulse and the second reference channel of the ground station equipment.

The second reference channel contains the same elements as are found in the intelligence channels, with the exception that no recording voltmeter is. provided. The output from the cathode follower in the second reference channel is applied as bias on a tube in the compensator |24 which, therefore. adds algebraically to the output of the cathode follower I 22 a correcting voltage component sufficient to modify the output from the cathode follower |22 by an amount exactly compensating for any change in the timing between the pulses I2 and I9. The result is that the recording voltmeter |26 records a corrected voltage. For example, if outside conditions should affect the equipment in the balloon in such a way as to shorten the delay periods of all the multivibrators, the second reference channel circuit -would operate to insert a plus correction tothe input of the recording voltmeter |26.

For calibration purposes and for setting the multivibrator I I4 so that it will lock on the pulse 26. I provide apparatus for automatically causing the multivibrator |I4 to sweep through its range of delay periods. In order to obtain the sweep effect, I provide a saw-tooth generator |30 which generates direct voltage varying in a sawtooth wave pattern and feeds through a switch tube |32 to the cathode follower |22. The sawtooth D. C. voltage applied to the cathode follower |22 causes the delay multivibrator II4 to produce l0 pulses of periods covering its full range. During its sweep there 'will inevitably come a time when the delay multivibrator emits a triggering pulse 26' which causes the early and late gate circuits' I|6 and |20 to apply pulses to the video gate circuits |08 and ||0 which latter pulses IIS and I2| will coincide with a humidity pulse 26 received from the buier and clipper circuit 106. It is again to be understood, however. that the range through which the delay multivibrator vsweeps is not wide enough to include any of the other pulses coming from the buffer and clipper |06. When the pulses from the early and late gate circuits do coincide with a pulse 26 from the Y vthe switch tube. i From then on the saw-tooth generator |30 is effectively cut out of the circuit and the signal pulses 26 take over and determine the timing of the delay multivibrator 4 vin the manner previously stated. The combination of the saw-tooth generator |30, the switch tube |32 and the D. C. amplifier |34 provides fully automatic sweeping of the delay multivibrator II4. However, I contemplate the provision, as an alternative, of a manual control device |36 by means of which the delay period of the multivibrator ||4 may be varied until it locks on a signal from the buffer and clipper. between the amplifier |34 and the switch tube |32 will indicate when that condition has been obtained, and the pulse 26 from the buffer and clipper circuit |06 will again take over and determine the period of the delay multivibrator I I4.

It is to be remembered that the delay multivibrator ||4 is in each instance triggered by the pulse I2 fed from vthe receiver |00 through the discriminator |02 and through the trigger circuit I I2. When I s'peak of'sweeping the delay period of the multivibrator II4, it is to be understood that the initiation of the pulses 26' of the multivibrator ||4 is in each case obtained from the buffer circuit ||2, and the action of the discriminator |02 is to supply -to the buffer circuit 2 only the pulses I2 originating in the relaxation oscillator I0 in the airborne unit.

The circuit of the ground station equipment The ground station unit has been discussed f fromthe functional standpoint without specific reference to the elements of the various circuits contained therein. As in the case of the airborne unit, it will be understood that there are many possible circuits which could be employed with comparable results, but I have designed a circuit for lthe ground station unit, which is the best form known to me for carrying out my invention. This circuit is shown in Figs. 8 and 9 and will now be discussed in detail.

As before stated, "the high-frequency receiver |00 may be of conventional design; any communications type receiver capable of covering the frequencies used may be employed, provided it does not introduce time lags in the signals received.

The discriminator |02 is organized about a double triode, such as, for example SSN?. The operation of the circuit is as follows. The first half A of the tube is normally in the conducting state,v The negative pulses from the receiver are applied to a grid of the tube A and cut it oi for a length A voltmeter I 35 in the line r Saaie .been charge 'pair 'of' series :connected :resistors: i

half of the triode 200 is utilized as a limiting circuit. Again the grid 204 is connected to the plate 205 so that the second half of the triode 200 also functions as a diode. The cathode 206 is connected to ground through a resistor 201 and connected to B+ through two series connected resistors 208 and 209. The resistors 201.

208 and 209 comprise a voltage divider fromwhich cathode voltage is obtained. The delay multivibrator |I4 is organized about a double triode 2l0 and will not be described in detail since it is identical with the circut used for the delay multivibrator in the airborne unit previously discussed. The grid of the second half of the multivibrator tube2l0 is connected to the plate 205 of the limiting triode 200 with theresult that the function of the limiter is to prevent changes in amplitude or width of the trigger pulse from the buffer from aiecting the period of the delay multivibrator.

The output from the delay multivibrator I4 is fed through a differentiating circuit H6 which, again, is identical with the diierentiator utilized in the airborne unit. The output pulse 26" of the l diierentiator H6 is fed to the grid cf a, buffer tube 2| I, comprising a conventionally connected triode which serves both as a buffer and as an amplier. The plate of the buier tube 2l I is connected to a condenser 2|2 which is connected in series with a resistor 2|3 to form a pulse sharpening differentiating circuit. The output of the differentiating circuit is taken from between the condenser 2I2 and the .resistor 2I3 and fed through a blocking condenser 2|4 into the early gate circuit l I8. i

The early gate circuit I|8`comprises a triode connected with elements forming a blocking osandi relate tra indue-; f

order to prevent distortion of the pulse form. The grid is grounded through a bias resistor 220, and the screen grid is grounded through a condenser 230 to eliminate-extraneous oscillations and parasitics. 'I'he screen receives voltage from B+. The suppressor grid of the pentode is inductively coupled to the plate of the early gate triode through a condenser 232 and a transformer 234. A transformer 236 is included in the plate circuit of' the pentode 220 to provide coupling between the video gate circuit |08 and the integrator I I2. The suppressor grid is connected to C through a resistance network to provide a xed negative voltage on the suppressor for preventing the 110W of plate current when a pulse reaches the control grid. 'I'he result is that the pentode 220 will conduct only-when a pulse 26 on the control grid coincides with a pulse I I9 on the suppressor grid. Both pulses are, of course, positive.

'I'he video gate circuits are identical, as before stated, the gate4 |08 being connected to the early gate IIB and the video gate H0 to the late gate |20.

The next unit comprises the integrating cir cuits H2 and H3, including apair of triodes, 240 and 242. The grid of the triode 240 is connected through a condenser 245 to the output of the video gate circuit |08, and the plate is tied to the cathode of the triode 242. The cathode of the triode 240 is grounded through a bias resistor 244 shunted by a condenser 246; and the c athode is connected to C. through a voltage divider 248.'-

Grid bias is obtained from C`V through a resistor 250. The plate of .the triode 242 is connected to B+ across a. voltage dividing network to provide stable plate voltage. The-grid-oi the triode 242 resister 22# is connected through a condenser 241 to the output of the video gate IIO and to a balance control potentiometer 252 later to be discussed.

Pulses from the video gates are stored on the condensers 245 and 241. The triodes 240 and 242 are normally closely balanced, and a constant D. C. voltage is taken off the cathode of the triode 242 and the plate of the triode 240. This output is applied to a large condenser 255 grounded on one side. If pulses reach the condensers 245 and 241 in the form shown in Fig. 5, that is to say, equal pulse potentials are developed on the two grids, the balance is maintained and the output voltage does notchange. If the signal pulse 26 rides more on the early gate pulse ||9 than on the late gate pulse |2I, the integrated pulse'potential from the condenser 245 on the grid of the triode 240 will be greater than the potential developed on the grid of the triode 242. ConsequentlyV the charge on the condenser 255 decreases because the triode-240 will be passing more current than the triode 242. Conversely if the signal 26 rides more on the late gate pulse I 2| than on the early gate pulse II9, the charge on the condenser 255 will be increased. Thus the D. C. output of the integrator circuits I I2 and I I3 is made to respond to the relative position of the signal pulse 26 in the cycle of pulses emitted from the airborne unit.

'I'he combined output of the integrator circuits is fed to a conventional cathode follower amplifier |22.

To maintain balance of the triodes 240 and 242 I provide a constant current pentode 251 conven- -etionally connected and including in its plate circuit the potentiometer 252. One end of the potentiometer 252 is connected to the cathode of the amplifier |22 to prevent unbalance of the integrator triodes resulting from shifts occurring in the period of thedelay multivibrator II and consequent changes in the output, from the integrator circuits.

The output from the cathode follower |22 is taken through a potentiometer 214 and applied back on the first grid of the delay multivibrator II4. As previously stated the trailing edge of the pulse of the delay multivibrator II4 deterpulses. As the cathode follower responds to a change in the relative position of the humidity pulse 26 and the gate pulses I I9 and |2 I, the portion of the output voltage which is applied back 7 262 connected to the output of the cathode follower of the second reference channelr circuit. A voltage divider is inserted before the screen grid of the tube 260 to reduce the voltage from the tube 262 to proper limits. As the period of the delay multivibrator of the second reference channel is varied by changes in the time between the pulse I2 and the pulse 19, va voltage proportional to the change appears on the screen grid ofthe tube 260. If the time between the pulses I2 and I9 shortens, the voltage on the screen swings more positive, and the output voltage from the cathode of the pentode 260 rises. The reverse occurs if the time between pulses increases. A potentiometer 264 is included in the cathode circuit of the tube 260, for calibrating purposes, the movable contact being connected to the recording voltmeter |26.

It win be understood that the control grid orthe tube 262 in the second reference channel is connected to the cathode of a cathode followery amplifier in the circuit of thevsecond reference channel and that the plate of the tube 262 feeds Y compensating voltage to the two other intelligence channel circuits in the same manner as it feeds the screen grid of the tube 260.

It is necessary to provide means for sweeping the delay multivibrator I |4 through its range of delay periods, when the equipment is started, so that the trailing edge of the multivibrator pulse will be fed through the early and late gate circuits |I8 and |20 and made to coincide with the appearance of a humidity pulse 26 reaching the published in 17937 by McGraw-Hill Book Comv mines the position of the early and late gate the switch tube |32.

pany. The generator |30 feeds through a double triode 210 connected back-to-back as a switch tube, the cathode of each half of the double triode being connected to the plate of the other half, and then to the grid of the cathode follower |22. A D. C. amplifier 34 is connected to the combined output of the video gate circuits |00 and H0. The amplifier |34 is conventional except for a large capacity cathode condenser 212 which smooths out the pulses' received from the video gate circuits. The amplifier output is applied to the grids of the tube 210, and the connections are such that when signals pass through the video gates, they are amplified and applied as D. C. voltage on the grids of the tube 210, the amplified voltage being sumcient to bias the tube 210 below cut off. Hence the flow from the saw-tooth generator |30 is cut ofi.

When signals do not reach the amplifier |34, the switch tube |32 feeds the saw-tooth output to the cathode follower amplifier |22. The output of the latter is taken'through a potentiometer 214, connected in a voltage divider network from the -cathode of the amplifier tube |22 to ground. and applied to the delay multivibrator IM. The setting of the potentiometer 21d in conjunction with a grid condenser 216 in the multivibrator circuit I|4 determines the range ofdelay periods. Therefore the saw-tooth `waves from the ampli- .fier |22 vary the voltage on the potentiometerl 214 and sweep the multivibrator IIt across its range of delay periods, each pulse originating, as before, from the trigger pulse from the buffer III.

When trigger pulses from the early and late gates ||8 and |20 coincide at the video gate circuits I08 and I|0 with a humidity pulse 26 from the buffer and clipper |06, the video gates conduct current and feed the amplifier |34 which cuts off Thereafter the pulses 26 take'control of the delay multivibrator I I4 in the manner above described. A mllliammeter |36 is connected in the plate circuit of the last tube in the D. C. amplifier |34. When the meter reading is low, the switch tube is cut off; when the meter reads high, the switch tube lets the saw-tooth voltage from the saw-tooth generator |30 contr'ol the delay multivibrator I I4.

The circuit including the D, C. amplifier |34, the saw-tooth generator |30, and the switch tube |32 provides for automatic sweeping of the delay multivibrator II4. For manual -control of the multivibrator, I provide a potentiometer 21B connected across a voltage dividing network from B-lto ground and to the cathode of the amplifier |22; a switch 280 is included in the line from the potentiometer 218 to provide for disconnecting it when the humidity pulses 26 have been synchronized with the early and late gate circuit pulses. The voltage through the potentiometer 21d is applied to affect the delay period of the multivibrator i it in the same manner as the output of the saw-tooth generator itil.

Those slrilled in the art will readily appreciate the necessity of providing appropriate test and Calibrating equipment such as voltmeters, ammeter, Oscilloscopes, etc. With their use the circuits may be readily adjusted and calibrated.

Having thus disclosed my invention, what l claim as new and desire to secure by Letters Patent of the United States is:

i. Meteorological apparatus comprising a transmitter arranged to emit fixed frequency reference signals and intelligence signals interposed in varying positions between each pair of reference signals, a receiver for said signals, a discriminator connected to said receiver and arranged to pass only the reference signals, a delay multivibrator connected to the output of the discriminator, early and late gate circuits connected to the output of said multivibrator, a clipper and buffer circuit connected to the output of the receiver, a pair of video gate circuits connected to the early and late gate circuits and to the buffer and clipper circuit, integrator circuits connected to said video gate circuits, a cathode follower ampler connected to the output of the integrator circuits and connected to the delay multivibrator, a voltage compensator circuit also connected to said cathode follower output, and a recording voltmeter connected to the output of said compensator.

2. Meteorological apparatus, comprising a delay multivibrator, an oscillator connected to trigger said multivibrator at fixed intervals, an element sensitive to a meteorological condition, means connected to said element and to said multivibrator for controlling the delay period in response to said condition, means for transmitting one signal when said multivibrator is triggered and a second signal when said delay period ends, means for receiving both signals, and means for measuring and recording the time between the two signals.

3. Apparatus of the class described comprising a receiver, a pair of video gate circuits fed from said receiver, a discriminator connected to said receiver and arranged to pass only pulses above a predetermined width, a delay multivibrator triggered from said disciminator, early and late gate circuits connected to said delay multivibrator and to said video gate circuits, integrating circuits connected to said video gate circuits, and a voltmeter connected to said integrators.

4. Apparatus of the class described as in claim 3 wherein a cathode follower amplier is connected between said integrators and said volt-l meter.

5. Apparatus of the class described comprising a radio transmitter, a rst delay multivibrator feeding said transmitter, an oscillator producing fixed frequency pulses triggering said delay multivibrator and feeding said transmitter, means responsive to a meteorological condition for controlling the period of said delay multivibrator, a receiver, a second delay multivibrator constructed to have a. period equal to that of the rst delay multivibrator, means connected to said receiver for feeding to the second multivibrator only the pulses transmitted directly from the oscillator, early and late gate circuits triggered by said second multivibrator, a pair of video gate circuits connected respectively to said early and late gate circuits, each oi said video gate circuits being also fed from the receiver and so arranged as to pass current only when pulses from the early and late gate circuits coincide with pulses from said receiver and transmitted from said first delay multivibrator, integrator circuits fed by said video gate circuits, a cathode follower amplifier fed jointly by said integrator circuits, a voltrneter connected to measure the output from the amplifier, and means connected to said cathode follower amplifier and said second delay multivibrator for controlling the period of the latter in response to the relative position oi the pulse from the first multivibrator with respect to the pulses from the early and the late gate circuits.

6. Apparatus of the class described comprisr ing means for transmitting a pair of timed reference pulses at a fixed rate, means for transmitting between pairs ci reference pulses a plurality of intelligence pulses each of which is timed relative to the reference pulses by an amount responsive to a meteorological condition, a receiver for all of the pulses, means responsive only to one of said reference pulses for producing a closely adjacent pair of gate pulses at intervals corresponding closely to the intervals between successive repetitions of a selected one of said intelligence pulses, means for recording a voitage, and means for4 applying to said recorder a voltage only when said pair of gate pulses coincides with said selected intelligence pulse.

7. The apparatus described in claim 6 with the addition of means responsive to variations in time elapsing between successive reference pulses and eiective to vary the timing of the gate pulses in order to automatically synchronize the selected intelligence pulse and said gate pulses.

8. Apparatus of the class described comprising a first buffer circuit, a delay multivibrator fed from said rst buler circuit, a differentiating circuit fed by said delay multivibrator, a pair of pulse-producing circuits, one of said pulseproducing circuits being triggered by said differentiating circuit and the second pulse-producing circuit being fed by the rst, a pair of gate circuits each of which is fed by one of said pulse-producing circuits, a second buffer circuit feeding both of said gate circuits, integrator circuits each of which is fed by one` of the gate circuits, and amplifier fed jointly by said integrators and feeding said multivibrator to control its delay period, and a voltmeter fed from said amplifier.

9.Apparatus of the class described comprising means for transmitting a pair of timed reference pulses at a xed rate, means for transmitting between pairs of reference pulses a pluralityV of intelligence pulses each of which is timed relative to the reference pulses by an amount responsive to a meteorological condition, a receiver for all of the pulses, means responsive only to one of said reference pulses for producing a closely adjacent pair of gate pulses at intervals corresponding closely to the intervals between successive repetitions of a selected one of said intelligence pulses, means for recording a voltage, means for applying to said recorder a voltage only when said pair of gate pulses coin- .l Meegos 17 cides with said selected intelligence pulse, and means responsive to shifts in time between said reference pulses for introducing a compensating voltage on said recorder.

10. Apparatus of the class described comprising means for transmitting a pair of timed reference pulses at a xed rate, means for transmitting between pairs of reference pulses a plurality of intelligence pulses each of which is timed relative to the reference pulses by an amount responsive to a meteorological condition, a receiver for all of the pulses, means responsive only to one of said reference pulses for producing a closely adjacent pair of gate pulses at intervals corresponding closely to the intervals between successive repetitions of a selected one of said intelligence pulses, means for recording a voltage, means for applying to said recorder a voltage only when said pair of gate pulses coincides with said selected intelligence pulse, and means for REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,027,367 Blair Jan. 14, 1936 2,216,161 Curtiss Oct. 1, 1940 2,381,009 Siderman Aug. '1, 1945 2,395,467 Deloraine Feb. 26, 1946 2,402,973 Moore ---.L July 2. l1948 2,403,210 Butement July 2, 1946 2,403,890

Johnson July 9, 1946 

